This study is designed to assess: l) comfortable speed of walking (C.S.W.), and 2) energy expenditure and oxygen consumption of high level lower extremity amputees (hip disarticulation and hemipelvectomy) during ambulation with or without prosthesis, and also at rest, breathing room air. Other parameters such as respiratory exchange ratio, etc., will also be calculated. These respiratory and metabolic measurements will be measured in a group of normal individuals age and sex matched.